Surface deformable imaging member of improved dark decay characteristics

ABSTRACT

An integral imaging member used for formation of a frost imaging pattern on the surface thereof is disclosed which comprises; a transparent substrate, a conductive layer over said substrate, an arsenic triselenide photoconductive layer, with a frostable thermoplastic layer on the outer surface of said member on which the frost image pattern is formed. Between the photoconductive and conductive layer a blocking layer is interposed to reduce dark decay characteristics of the photoconductive layer upon charging thereof, said layer comprising a phenoxy or epoxy resin with a thickness of between about 200 and 4,000 Angstroms.

[ 1 June 25, 1974 SURFACE DEFORMABLE IMAGING MEMBEROF IMPROVED DARK DECAY CHARACTERISTICS [75] Inventor: Michael P. Trubisky, Fairport, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Sept. 5, 1972 [21] Appl. No.: 286,483

[52] US. Cl. 96/l.5, 96/1.1 [51] Int. Cl 603g 5/10 [58] Field of Search 96/l.1, 1.5, 1 R

[56] References Cited UNITED STATES PATENTS 3,196,008 7/1965 Mihajlov et a1 96/1.1 3,196,011 7/1965 Gunther et al.... 96/].1 3,214,272 10/1965 Ploke 96/l.1

3,715,207 2/1973 Ciccarelli 96/15 3,729,310 4/1973 Ciccarelli 96/1.1

Primary Examiner-Ronald H. Smith Assistant ExaminerJohn L. Goodrow Attorney, Agent, or FirmJames J. Ralabate; James P. OSullivan; Donald M. MacKay 5 7] ABSTRACT An integral imaging member used for formation of a frost imaging pattern on the surface thereof is dis closed which comprises; a transparent substrate, a conductive layer over said substrate, an arsenic triselenide photoconductive layer, with a frostable thermoplastic layer on the outer surface of said member on which the frost image pattern is formed. Between the photoconductive and conductive layer a blocking layer is interposed to reduce dark decay characteristics of the photoconductive layer upon charging thereof, said layer comprising a phenoxy or epoxy resin with a thickness of between about 200 and 4,000 Angstroms.

14 Claims, 1 Drawing Figure SURFACE DEFORMABLE IMAGINGMEMBER OF IMPROVED DARK DECAY CHARACTERISTICS This invention broadly relates to an imaging member used for the formation of images on surface deformable thermoplastic materials having a charged photoconductive layer which is characterized by low dark decay characteristics.

It is known to form image patterns on surface deformable thermoplastic materials by two distinct methods. The first of these is known as relief imaging and is described in U.S. Pat. Nos. 3,055,006; 3,063,872 and 3,113,179. The other method is referred to as frost imaging and is described for example, in U.S. Pat. Nos. 3,196,008; 3,196,01 l 'and'3,258,336. While'both ofthe above methods form image patterns by deformation of a thermoplastic material responsive to electrostatic forces, a fundamental distinction between the two methods is that image formation in the first method occurs on uniformly charged areas as a uniform distribution of surface folds or wrinkles whereas image formation in the relief method is dependent on electrostatic gradients thus forming a single line deformation along the edgedefined by a charge gradient. Relief imaging will therefore not'occur where there is uniform charge distribution. The present invention is primarily directed to a frost type imaging system and member.

In the usual frost method of surface deformation imaging, a latent electrostatic image or charge pattern is formed on an insulating film which is softenable, as by the application of heat or solvent vaponthis being specifically referred to as the heat deformable member of the imaging device. Specifically, the latent electrostatic image can be formed by the'use of a suitable photoconductive' layer beneath the deformable member, which upon exposure to radiation generates holeelectron pairs. Depending on the type of photoconductor and the applied electrical field, the uniformly charged deformable member is charge dissipated in image configuration by the transport of a specific charge through the photoconductive material following exposure to radiation to form a latent image in the photoconductive material. Following exposure, the surface of the deformable layer is recharged with a corona device to form a surface electrostatic latent image corresponding to the electrostatic latent image formed in the photoconductive layer following light exposure.

After formation of the surface latent electrostatic image, the film is softened until the electrostatic forces of the charge pattern exceeds the viscosity forces of the film. When this threshold condition is reached, a series of very small surface folds or wrinkles are spontaneously formed on the film surface, the depth of the wrinkles in a particular area of the film being generally dependent upon the intensity of light exposure and charge in the area. This gives the image a frosted appear.-

ance. I

Alternatively, the film may be softened prior to application of the uniform charge pattern if the film remains sufficiently insulated in a softened state to hold the charge. The frost image is set or fixed by allowing the film to reharden. In a reversible frost system, it is usually desirable to later erase the fixed image after use by resoftening the thermoplastic film and maintaining a sufficiently low viscosity for appropriate periods of time to permit surface tension forces to smooth the film surface. By erasing the surface deformation image at a temperature substantially above the films softening point and returning the film to its original condition, the step of the frost" imaging process may be typically repeated, these comprising in sequence charging, exposure, recharging then again erasing the deformable image, for another repetitive cycle.

A frost imaging member as envisioned in the present invention, generally comprises a transparent substrate, an overlying transparent conductive layer, a photoconductive layer and the deformable layer used for frosting. More specifically, it was determined that when a p-type photoconductive material such as vitreous arsenic triselenide (As se was employed as the photoconductive layer, with this type of material having the ability to transport holes in preference to electrons, that two problems resulted; first of all, it was found that the transparent conductive layer injected holes into the photoconductive layer, thereby giving rise to objectionally high dark decay, when the deformable layer is charged negatively, and secondly, it was determined that structural integrity of the device is weakened by poor adherence of the photoconductive material to the transparent conductive layer.

It is therefore determined that the above two problems could be obviated by the incorporation in the recited frost device of a blocking adhesive layer to reduce injection of holes into the photoconductive material by the adjacent conductive layer thus reducing the dark decay thereof, as well as to improve adhesion between the layers.

SUMMARY OF THE INVENTION The present invention therefore relates to an imaging member, suitable for frost imaging which comprises a transparent substrate, an overlying transparent, conductive layer, with a blocking layer between said conductive layer and an arsenic triselenide photoconductive material which overlays the conductive layer. The top layer of the recited device comprises a frostable thermoplastic material as is normally employed in frost imaging. Optionally, a screen of appropriate spatial frequency can be employed in the above device to force the frostable thermoplastic material to deform into its quasi-resonant form.

The above described blocking layer of the device of the instant invention comprises a high molecular weight resinous material selected from the group of epoxy and phenoxy resins to both effectively reduce dark decay of the described photoconductor and provide adhesive bonding of the photoconductive material to the conductive layer.

It is therefore an object of the present invention to provide an imaging device of improved characteristics for surface deformation imaging processes.

Another object of the instant invention is elimination of excessive dark decay in such an imaging device when a p-type photoconductive material is employed as an integral part thereof.

Another object of the instant invention concerns the provision of a frost imaging device of good structural integrity as well as good electrical characteristics.

These and other objects are accomplished in accordance with the present invention by the following description thereof appended by the accompanying examples.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the imaging member of the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the transparent substrate layer 2 of the imaging member set forth, comprises a suitable support material, which is transparent to a wide range of actinic radiation, preferably glass. The particular material used for this layer or the thickness thereof is not critical to functional properties of the instant imaging member, but rather is based principally on the support and optical properties provided The conductive layer 3 which overlays the support layer comprises a conductive layer, of a prescribed thickness, which is essentially transparent and which has a wide range of spectral transmission in the actinic region of the spectrum. The thickness of the described layer will vary depending on the specific material employed but will generally be between 100 and 200 Angstroms. Suitable materials, although not limiting, include metallic substances such as chromium or gold, mixtures thereof or mixtures of these metals with various metallic or non-metallic oxides such as a bismuth oxide (Bi O etc. The specific substance employed as the conductive layer of the instant imaging member is not intended to be limiting, providing it is essentially transparent at a thickness which provides sufficient conductivity, as well as mechanical strength.

The photoconductive layer 4 adjacent to the conductive layer comprises in the context of a present invention, a p-type of photoconductive material that will transport holes in preference to electrons, preferably arsenic triselenide (As Se Therefore, with exposure being carried out through the transparent substrate of the instant device, the overlying deformable layer 6, is charged negatively so that the more mobile holes will be transported to the deformable layerphotoconductive layer interface upon imagewise exposure to selectively lower the potential across the photoconductive layer and upon recharging create surficial deformations or frosting on layer 6. The thickness of the described photoconductive layer is not critical to the practice of the instant invention although it is preferably between about to microns.

Overlying the photoconductive layer 4 is deformable layer 6 which comprises a frostable thermoplastic material selected from among those which are suitable for this purpose and which are described in US. Pat. No. 3,196,01 l. The specific frostable thermoplastic material employed is not considered at all critical for the practice of the instant invention and any one suitable for this purpose may be employed. The thickness ofthe deformable layer will be on the order of about 1 to 2 microns, although the specific thickness will be dependent on factors such as the specific material employed, reusability, charging, and/or other functional characteristics of the device.

Optically, in the present imaging device a suitable screen 5 may be employed as shown in FIG. 1 between the conductive layer and the transparent substrate. The use of a screen with appropriate spatial frequency permits one to modulate the imaging light to produce a sinusoidal electrostatic field which forces the thermoplastic layer into its quasi-resonant" form of exposure.

A screen suitable for the instant device comprises a chromium screen between the substrate and conductive layer.

While the above described component layers and materials could be combined to yield an effective frost imaging device, it was determined that several problems existed with such a device. Among these were not only difficulties in securing adhesion between the photoconductive and transparent conductive layer, but the transparent conducting layer will also inject holes into the bulk of the photoconductor, when the deformable layer is negatively charged, thus increasing dark decay of the photoconductive material to an unacceptable level. It was found that both of these problems could be overcome by the incorporation of a layer between the photoconductive and conductive layer to provide ad hesion as well as block the injection of holes from the conductive layer into the bulk of the photoconductor. Referring specifically to FIG. 1 the blocking layer 7 as illustrated, is interposed between the photoconductive and conductive layers. The blocking layer must comprise a material having not only good adhesive qualities but the ability to block the holes long enough for the recharging step of a typical frost imaging cycle to take place. On the other hand, to provide a hole trapping mechanism which traps the holes too well, would make the frosted image difficult to erase. The specific materials which have been found suitable for this purpose include epoxy or phenoxy type resins, the epoxy resins suited for this purpose being characterized by a molecular weight of between about 5,000 and 8,000, and the phenoxy resins being characterized by repetitive molecular units of the type;

Specific resins of both type which have been found suitable include Araldite 6099 epoxy resin having a molecular weight of about 65,000 available from CIBA Corporation, Summit, N.J., and Bakelite Phenoxy PAHJ with a molecular weight of about 35,000 available from Union Carbide Corporation, New York, NY. Either of these types of materials perform extremely well in producing good adhesive bonds between the photoconductor and the conductive layer without the photoconductor cracking.

The thickness of the blocking layer which comprises the above materials in the instant imaging device is critically defined between about 200 and 4,000 Angstrom units. This particular thickness range has been found to be particularly effective in reducing dark decay of the arsenic triselenide photoconductive layer of the instant invention to an acceptable level. The preferred thickness range of the blocking layer will be about 500 to 1,500 Angstrom units. If the thickness varies from within this range, for example if it is below the range, it becomes ineffective to block the injection of holes long enough for the recharging step which forms a surface electrostatic latent image corresponding to that formed in the photoconductive layer following light exposure. On the other hand, if the thickness is above of this range it becomes difficult to erase the image and permit repetitive use.

Having described the invention above, the following examples are given to more fully illustrate specific embodiments thereof. The examples are given for illustrative purposes only and are not intended to be limiting on the scope of the invention.

EXAMPLE 1 A frost imaging device as defined in the instant invention was prepared as follows: a piece of glass having a thickness of about one-fourth inch was selected as the transparent substrate layer, which was cleansed by soaking in chromic acid for several minutes, then rinsed with distilled water. Following this, the substrate was ultrasonically cleansed for 2 to 5 minutes.

A chromium optical screen was formed as follows; a layer of about 0.04 microns of photoresist was coated over the glass substrate, after drying the plate was exposed by an interference pattern generated by an Argon ion laser having an output at a wavelength of 4,579 A and a beam sweep system. The latent pattern was spraydeveloped; washed and dried. The photoresist was coated with chromium by vacuum evaporation and the remaining photoresist with excess-chromium removed. The screened substrate was overcoated with a conductive gold layer of about 100-200 Angstrom units in thickness, which was vacuum evaporated over the screened substrate. Thereafter the blocking layer comprising either the epoxy or phenoxy type of resin was applied by uniformly applying a dip coating over the conductive layer. The photoconductive layer was then bonded to the conductive layer by vacuum evaporation of arsenic triselenide (As Se to the composite member in a thickness of between about to microns. After application of the photoconductor, the deformable frostable thermoplastic layer was applied by dip coating the imaging member to yield a frostable thermoplastic layer about 1 to 2 microns in thickness.

' EXAMPLE 2 To determine the effectiveness of the described blocking layer in reducing dark decay of the arsenic triselenide photoconductive layer, four plates were prepared as generally described in Example 1, but without the chromium optical screen or deformable thermoplastic layer. All of the described plates were charged negatively on the top surface with a conventional corona charging device to a field of about 12 volts/micron. Following charging, the percentage loss in potential in the first five seconds after charging of the plate is measured as being representative of the dark decay of the charged arsenic triselenide layer of the imaging member. The four plates were as follows:

Plate A. a substrate of glass overcoated with a gold layer 180 Angstrom units thick, with a 10 micron thick layer of arsenic triselenide overthe gold layer.

Plate B. a substrate of glass overcoated with a conductive layer of gold 180 Angstroms thick, the conductive layer overcoated with a blocking layer of Araldite 6099 Epoxy Resin 220 Angstroms thick, with a 10 micron arsenic triselenide layer over the blocking layer.

Plate C. a substrate of glass overcoated with a conductive layer of gold, 180 Angstroms thick, the conductive layer being overcoated with a blocking layer of Araldite 609 9 Epoxy Resin, 750 Angstroms in thick- TABLE 1 ORIGINAL POTENTIAL PLATE v0) VOLTS DARK DECAY 5 sec) A 133 32.0% B 3.3% c 110 2.3% D 123 2.4%

It may be seen from the data in Table 1 that the use of the epoxy resin blocking layer significantly reduces dark decay of the negatively charged arsenic triselenide photoconductive layer thus effectively preventing charge injection into the bulk of the photoconductive layer by the transparent conductive layer.

EXAMPLE 3 Two plates were prepared as described in Example 1 and tested as in Example 2, each plate having a glass substrate with a Angstrom thick conductive layer of gold thereover, a blocking layer over the conductive layer, and with a 15 micron thick layer of arsenic triselenide photoconductor. The blocking layer of one plate designated as Plate E, comprised Phenoxy PAHJ resin, 870 Angstroms in thickness, while the second plate designated as Plate F had a blocking layer comprising Phenoxy PAHJ resin 1,000 Angstroms in thickness. Following negative charging of the two imaging members with a corona charging device, the percentage loss in original charging potential in 5 seconds was measured and expressed as dark decay of the respective plates: This being as follows:

ORlGlNAL POTENTIAL PLATE (V0) VOLTS DARK DECAY (5 sec) E 198 5.l% F 209 4.3%

It may therefore be seen that the described phenoxy resin blocking layer is efiective insofar as reducing dark decay of the negatively charged arsenic triselenide photoconductive layer to an acceptable level.

While the invention has been described in terms of preferred embodiments, it is to be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adopt a particular situation or material to the teaching of the invention without departing from its essential teachings.

What is claimed is:

1. An integral imaging member used for the formation of a frost imaging pattern on the surface of said member comprising; a transparent substrate, a transparent conductive layer overlaying said substrate, a photoconductive layer consisting essentially of arsenic triselenide adjacent to said conductive layer, a blocking layer between said photoconductive layer and said conductive layer consisting essentially of a material selected from the group consisting of epoxy and phenoxy resins with a thickness between about 200 and 4,000 Angstroms, and a frostable thermoplastic layer on the surface of said member. 1

2. An imaging member as set forth in claim 1 wherein the thickness of said blocking layer is between about 1,000 to 1,500 Angstroms.

3. An imaging member as set forth in claim 1 wherein said photoconductive layer has a thickness of between about 10 to microns.

4. An imaging member as set forth in claim 1 wherein said frostable thermoplastic layer has a thickness of between about 1 to 2 microns.

5. An imaging member as set forth in claim 1 wherein said substrate comprises glass.

6. An imaging member as set forth in claim 1 wherein said transparent conductive layer comprises a material selected from the group consisting of gold, chromium, metallic oxides, and mixtures thereof.

7. An imaging member as set forth in claim 1 wherein said conductive layer has a thickness of between about 100 and 200 Angstroms.

8. An integral imaging member used for the formation of a frost imaging pattern on the surface of said member comprising; a transparent substrate, a metallic spatial frequency screen overlaying said substrate, with a transparent conductive layer over said screen, a photoconductive layer consisting essentially of arsenic triselenide adjacent to said conductive layer, a blocking layer between said photoconductive layer and said conductive layer consisting essentially of a material selected from the group consisting of epoxy and phenoxy resins with a thickness between about 200 and 4,000 Angstroms and a frostable thermoplastic layer on the surface of said member.

9. An imaging member as set forth in claim 8 wherein said metallic screen is a chromium screen.

10. An imaging member as set forth in claim 8 wherein the thickness of said blocking layer is between about 500 to 1,500 Angstroms.

11. An imaging member as set forth in claim 8 wherein said photoconductive layer has a thickness of between about 10 to 20 microns.

12. An imaging member as set forth in claim 8 wherein said frostable thermoplastic layer has a thickness of between about 1 to 2 microns.

13. An imaging member as set forth in claim 8 wherein said transparent conductive layer comprises a material selected from the group consisting of gold, chromium, metallic oxides, and mixtures thereof with a thickness of between about to 200 Angstroms.

14. An integral imaging member used for the formation of a frost imaging pattern on the surface of said member comprising; a transparent substrate, a transparent conductive layer overlaying said substrate, with a photoconductive layer overlaying said conductive layer consisting essentially of arsenic triselenide having a thickness of between about 10 and 20 microns, a layer with a thickness between about 500 and l,500 Angstroms between said photoconductive and conductive layers consisting essentially of a material selected from the group consisting of epoxy and phenoxy resins, said layer reducing dark decay of said photoconductive layer to anacceptable level upon charging thereof, said member further having a frostable thermoplastic layer over said photoconductive layer and on the outer surface of said member. 

2. An imaging member as set forth in claim 1 wherein the thickness of said blocking layer is between about 1,000 to 1,500 Angstroms.
 3. An imaging member as set forth in claim 1 wherein said photoconductive layer has a thickness of between about 10 to 20 microns.
 4. An imaging member as set forth in claim 1 wherein said frostable thermoplastic layer has a thickness of between about 1 to 2 microns.
 5. An imaging member as set forth in claim 1 wherein said substrate comprises glass.
 6. An imaging member as set forth in claim 1 wherein said transparent conductive layer comprises a material selected from the group consisting of gold, chromium, metallic oxides, and mixtures thereof.
 7. An imaging member as set forth in claim 1 wherein said conductive layer has a thickness of between about 100 and 200 Angstroms.
 8. An integral imaging member used for the formation of a frost imaging pattern on the surface of said member comprising; a transparent substrate, a metallic spatial frequency screen overlaying said substrate, with a transparent conductive layer over said screen, a photoconductive layer consisting essentially of arsenic triselenide adjacent to said conductive layer, a blocking layer between said photoconductive layer and said conductive layer consisting essentially of a material selected from the group consisting of epoxy and phenoxy resins with a thickness between about 200 and 4,000 Angstroms and a frostable thermoplastic layer on the surface of said member.
 9. An imaging member as set forth in claim 8 wherein said metallic screen is a chromium screen.
 10. An imaging member as set forth in claim 8 wherein the thickness of said blocking layer is between about 500 to 1,500 Angstroms.
 11. An imaging member as set forth in claim 8 wherein said photoconductive layer has a thickness of between about 10 to 20 microns.
 12. An imaging member as set forth in claim 8 wherein said frostable thermoplastic layer has a thickness of between about 1 to 2 microns.
 13. An imaging member as set forth in claim 8 wherein said transparent conductive layer comprises a material selected from the group consisting of gold, chromium, metallic oxides, and mixtures thereof with a thickness of between about 100 to 200 Angstroms.
 14. An integral imaging member used for the formation of a frost imaging patterN on the surface of said member comprising; a transparent substrate, a transparent conductive layer overlaying said substrate, with a photoconductive layer overlaying said conductive layer consisting essentially of arsenic triselenide having a thickness of between about 10 and 20 microns, a layer with a thickness between about 500 and 1,500 Angstroms between said photoconductive and conductive layers consisting essentially of a material selected from the group consisting of epoxy and phenoxy resins, said layer reducing dark decay of said photoconductive layer to an acceptable level upon charging thereof, said member further having a frostable thermoplastic layer over said photoconductive layer and on the outer surface of said member. 